Don't have an existing example for you, due to the fact that I'm a newbie to this entire world of GEF\EMF\Eclipse infras...
But I can tell you it's very much possible though not the easiest thing to do, I'll share my process hopefully will help you.
I started out with having a semi-working GEF editor and an EMF model that was specific for the GEF view. I changed the model to the meet the Business/Real Life/Spoken model.
At that point of course nothing worked; so after a few failed attempts I went on and built another abstraction layer of my own, that meets the following:
1. Built and translated from/to the model language (and it has the knowledge into how)
2. The objects together build the "GEF-model"
3. Main repository of all working objects in a session (not a must but makes life easier)

following this most, but not all, of the GEF code was left unchanged, kept working, and thought to be working with the direct model.